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• Intruders may gain access through unprotected openings or
have the technical sophistication to bypass an alarm sensor or
disconnect an alarm warning device.
• Intrusion detectors (e.g. passive infrared detectors), smoke
detectors, and many other sensing devices will not work
without power. Battery operated devices will not work
without batteries, with dead batteries, or if the batteries are
not put in properly. Devices powered solely by AC will not
work if their AC power supply is cut off for any reason,
however briefly.
• A user may not be able to reach a P.A. or emergency button
quickly enough.
• While smoke detectors have played a key role in reducing
residential fire deaths, they may not activate or provide early
warning for a variety of reasons in as many as 35% of all
fires. Some of the reasons smoke detectors used in
conjunction with this System may not work are as follows.
Smoke detectors may have been improperly installed and
positioned. Smoke detectors may not sense fires that start
where smoke cannot reach the detectors, such as in chimneys,
in walls, or roofs, or on the other side of closed doors.
Smoke detectors also may not sense a fire on another level of
a residence or building. A second floor detector, for example,
may not sense a first floor or basement fire. Moreover,
smoke detectors have sensing limitations. No smoke detector
can sense every kind of fire every time. In general, detectors
may not always warn about fires caused by carelessness and
safety hazards like smoking in bed, violent explosions,
escaping gas, improper storage or flammable materials,
overloaded electrical circuits, children playing with matches,
or arson. Depending on the nature of the fire and/or the
location of the smoke detectors, the detector, even if it
operates as anticipated, may not provide sufficient warning to
allow all occupants to escape in time to prevent injury or
death.
• Passive Infrared Motion Detectors can only detect intrusion
within the designed ranges as diagrammed in their installation
manual. Passive Infrared Detectors do not provide
volumetric area protection. They do create multiple beams of
protection, and intrusion can only be detected in unobstructed
areas covered by the beams. They cannot detect motion or
intrusion that takes place behind walls, ceilings, floors,
closed doors, glass partitions, glass doors, or windows.
Mechanical tampering, masking, painting or spraying of any
material on the mirrors, windows or any part of the optical
system can reduce their detection ability. Passive Infrared
Detectors sense changes in temperature; however, as the
ambient temperature of the protected area approaches the
temperature range of 32–40 °C, the detection performance
can decrease.
• Alarm warning devices such as sirens, bells or horns may not
alert people or wake up sleepers who are located on the other
side of a closed or partly open doors. If warning device sound
on a different level of the residence from the bedrooms, then
they are less likely to waken or alert people inside the
bedrooms. Even persons who are awake may not hear the
warning if the alarm is muffle by noise from a stereo, air
conditioner or other appliances, or by passing traffic. Finally,
alarm warning devices, however loud, may not warn hearing-
impaired people or waken deep sleepers.
• Telephone lines needed to transmit alarm signals from a
premises to a central monitoring station may be out of